Method of and apparatus for extending and reducing thickness of a metallic band

ABSTRACT

A metallic band is subjected to a longitudinal tension equal to at most 80 percent of its mean tensile strength as it is passed through a plurality of bending units. In the units the band is bent back and forth through increasingly smaller radii of curvature causing lowering of the band&#39;&#39;s elastic limit at the bend and plastic flow and elongation thereat. The band engages each roll over an arc preferably greater than 5* and the diameter D of each roll or of each set of roll is calculated according to the formula:

United States Patent [1 1 Noe [ Dec. 11, 1973 METHOD or AND APPARATUSFOR EXTENDING AND REDUCING THICKNESS or A METALLIC EAND [75] Inventor:Oskar No,Mulheim/Rhur, Germany [73] Assignee: Firma BWG Bergwerk-undWalzwerk-Maschinenbau Gmbli, Duisburg, Germany 221 Filed: July 7,1972

[21] Appl. No.: 269,775

[30] Foreign Application Priority Data July 7, 1971 Germany P 21 34405.8

52 Us. Cl. 72/205, 72/160 [51] Int. Cl B21b 39/08 [58] Field of Search72/205, 160, 162, 72/165 [56] References Cited UNlTED STATES PATENTS2,060,400 11/1936 Niemann 72/160 X 3,605,470 9/1971 Polakowski 72/163Primary Examiner--Milton S. Mehr Attorney-Karl F. Ross [57] ABSTRACT Ametallic band is subjected to a longitudinal tension equal to at most 80percent of its mean tensile strength as it is passed through a pluralityof bending units. in the units the band is bent back and forth throughincreasingly smaller radii of curvature causing lowering of the bandselastic limit at the bend and plastic flow and elongation thereat. Theband engages each roll over an are preferably greater than 5 and thediameter D of each roll or of each set of roll is calculated accordingto the formula:

D l/( 1), wherein h is the thickness of the band in cm, E is the modulusof elasticity of the band in kg/cm, K is a constant between 25 and 50,and kp is the mean tensile strength of the band in kg/cm. The stripengages each roller over an arc which is greater than 5, while theimaginary contact with this roller is greater than 25.

11 Claims, 5 Drawing Figures ZMENTEB SEC 11 1975 3771.532 sum wasPATENTED DEC 3 1 I975 3.711.532 SHET 2 BF 5 PATENTEI] DEC 1 1 1975 SHEET3 BF 5 FMENTEUDECH I975 3777.532 SHEET NF 5 METHOD OFAND APPARATUSFOREXTEND ING AND REDUCING THICKNESS OF A METALLIC BAND FIELD or THEINVENTION Thepresentinvention relates'toa method of elongating andreducing the cross-section *ofa metallic band and, more particularly,to'a "method of andapparatus for cold-treating a sheet-metal strip tomake it longer and thinner.

BACKGROUND OF THE INVENTION A sheet-metal band or strip is customarilymade thinner and longer by the process of cold-rolling wherein pairimmediately upstreamhThe work done by the rolls is consumedapproximately one-half for plastic deformation of the band, and one-halfin the production of useless heat of compression which must be conductedaway from the work to prevent the temperature rise thereof beyond anoptimal maximum. Thus such a system is highly wasteful of energy.

In addition the rolls are extremely expensive and require frequentreplacementand/or refinishing because, under the enormous compressiveforces to which they are subjected, they tend to "wear rapidly. It iscommon practice to back up the working rolls which define the workinggap with large-diameter support rolls. The working rolls often must bereplaced daily in a large cold-rolling installation, and the supportrolls every few weeks. Thus the rolling string is often out of serviceand the output of the mill is limited.

Customary rolling installations are controlled by highly expensivedevices which regulate the working gaps and circulate the variouscoolants, keeping these coolants, which are necessarily sprayed on theworkpiece in the gaps, clean and cool. In tandem strings with fourormore roll sets the power consumption is often in the neighborhood of15,000 to 20,000 kilowatts, with very heavy-duty transformer switchingand rectifi cation stations necessary. The cost of'the electricalcontrol and power installations may thus approach the cost of themechanical parts of the system.

It is also known to stretch a sheet-metal band by passing back and forthbetween a pair of drums. This method has never met with commercialsuccess since the operation is inherently discontinuous, thereby not forplastic deformation of a strip in a typical straightening operation. Inthis method the band to be straightened is passed under tensionthrough'successive setsof rollers each of which bends it inadirectionoppositeto the bend direction of the preceding pair. However each bendis through a larger radius of curvature than the previous one so that bythe time the band passes through the entire group of bending rollersit'is straight.

Such a method is perfectly efficient for straightening a bent band buthas little effect on either the length, width, or thickness of the band.

Y OBJECTS or THE INVENTION lt'is therefore an object of the presentinvention to provide an improved method of reducing the thickness of aband.

"Another object is the provision of'a method of and apparatus forelongating a band while reducingits thickness.

Yetanother'object is to provide an installation which issimple'andinexpensive tomake and operate.

SUMMARY OFTHE INVENTION l'attain these objectsaccorc'ling tothe'presentinvention in al'engthening system wherein the band is bentbackand "forth through eversmaller radii of curvature whileit'is'longitudinally tensionedwith a force below its elastic limit ormean tensile strength. The latter is "defined as the tensile forcewhich, in the absence of bending or other working is sufficient byitself to permane'ntly stretch the strip.

Ithas' been foundfthat such bending reduces the elastic limitlocally, atthe bend, to permit plastic flow and elongation in this region withoutany necessity of compressing or squeezing the band. The bending rollersare staggered alongthe path of the band, exerting no compressive forceon the band, so that they are not subject to the considerableforcespresent ina rolling opera- I tionJTherefOre the heat buildupan'd wear ingeneral is reduced to a fraction of what it is in a'cold-rolling millwhile 3 of freedom for working are obtained as opposedto the 1 offreedom (transverse force) of the rolling mill.

According to another feature of this invention, each bending roll issituated so with respect to the rolls immediately upstream anddownstream that a pair of imaginaryplanes both crossing the workpiecepath and tangentto the middle roller and each tangent to a respectiveflanking roller define an arc B of at least 25 on the middle rollerbetween their contact lines thereon. At the same time, however, the bandonly engages an are 'a slightly larger than 5 on the this middle roll.Were the strip perfectly elastic and of zero thickness it would liealong thearc a, but its inherent rigidity makesthisiinpossible. This arca is increased for increased stretching of the band, and decreased ifless stretching is desired. In reality the arc a and the arc Bareinterdependent so that they increase and decrease together accordingto a function which is primarily deter'rnined by the rigidity of thestrip. In addition, the strip tension is a factor which determines theangular size of these arcs; the greater the longitudinal tension in theband, the greater these arcs will be. It should be noted that the actualcontact angle [3 here is much smaller than the theoretical contact anglea. In addition, theoretical contact arc or is actually defined by twoplanes as described above which are, however, parallelto planes tangentto the'upstream and downstream rollers, and spaced from these planes bya distaiice equal to the workpiece thickness.

The diameter of each roll is calculated with the formula:

D (h E)/(K k5) wherein D is the rolls diameter, h is the band thicknessin cm, E is the modulus of elasticity in kg/cm k is the mean tensilestrength in kg/cm, and K is a constant from 25 to 50. According toanother feature of the invention a longitudinal tension is exerted onthe band which is of the order of 80 percent at most of the band meantensile strength.

Such an arrangement functions at high or low throughput speeds so thatit may be combined with galvanizing equipment or any other continuousoperations. It is also possible to stop the band and start it up againwith no noticeable effect on the finished product. Advantageously theband after such stretching is immediately subjected to a straighteningoperation, and even to a cold-rolling operation to eliminate any minorirregularities in thickness.

Since a relatively small amount of the energy exerted is transformedinto heat in comparison to the amount working to stretch the band, thedevice is highly efficient. No complicated cooling arrangement need beprovided, neither need any complicated devices to regulate thepositioning of the rolls be connected to the apparatus.

The rolls can, according to another feature of this invention, be ofconstantly decreasing diameter in the direction of workpiece travel.Alternately they can be arranged in groups of four or more rollers allof the same size, with the downstream group smaller. The roll size caneven decrease in each group, with the furthest downstream roll of onegroup being slightly larger than the furthest upstream roll of the nextgroup downstream. In any case it has been found advantageous accordingto yet another feature of the present invention to provide auxiliarydrive or advancing means between each two groups to ensure good advanceof the band.

DESCRIPTION OF THE DRAWING The above and other objects, features, andadvantages will become apparent from the following description,reference being made to the accompanying draw- SPECIFIC DESCRIPTION Asshown in FIG. 1 a steel band 18 is unwound from a braked drum 1 andeventually wound up on a driven drum 2, passing in a transport direction29 through the apparatus. A shear 3 and a welding device 4 are providedimmediately downstream of the drum 1 in order to cut off the end of thisband 18 and attach the leading edge of another such band thereto.Another such shear 5 is provided immediately upstream of the takeup drum2. Two gripping and driving arrangements 6 and 7 are provided at theupstream and downstream ends, respectively, of the apparatus, and areequipped with respective drive motors 6a and 7a which drive the upstreamdevice 6 slower than the downstream one, the speed differential beingsufficient to stress the band 18 in direction 29 to at most 80 percentof its mean tensile strength. My copending application Ser. No. 139,575,filed May 3, 1971 and my U.S. Pat. No. 3,559,431 describe drivessuitable for use with this invention.

Between the drives 6 and 7 the band I8 runs through six different groups8fof rolls 9 14 respectively. The rolls 9 are of greater diameter thanthe rolls It) and so on with the rolls 14 being the smallest. Largedriven rolls 15a 15e separate the bending units 8a 8f from one another.The furthest downstream bending unit 8f is followed by a pair ofstraighteners 16a and 16b of conventional type flanking a conventionalcold-rolling unit 17 serving to eliminate any minor imperfections in theband 18.

FIGS. 3 and 4 show the bending units 8a 8c in greater detail, with theunit 8b shown in its entirety. The rolls 10 of this unit comprise threeupper rolls 10a, 10a" and IOa, and two lower rolls lllb and 10b". Theroll 10a is larger than the roll 10b, with the roll 10a being thesmallest. In addition the roll Mia is smaller than the immediatelypreceding roll 9a and the roll I0a' is larger than the following rollIla.

All of the upper rolls 10a Itla' are supported on rollers on flangesformed on a vertically displaceable framework 25 and the lower rollers10b and 10b" are supported on rollers 10d carried on flanges formed onthe frame 30 of the device. A pair of hydraulic cylinders 26 canvertically displace the upstream end of the framework 25 and anotherpair of double-acting cylinders 27 support the downstream end. Sincerolls 10b and 10b" are rotatable about respective axes lying in a commonhorizontal plane, and the rotation axes of the rolls 10a 10a arecoplanar and parallel to the framework support 25, tilting of thesupport 25 by the cylinders 26 and 27 to the horizontal will change thegapping of the rolls of the bending bending unit 8b. Advantageously theleading end of the beam 25 is depressed by the cylinder 26 less than thetrailing end to ensure a tighter bend at this trailing end. Also when anew workpiece 18 is to be threaded through the apparatus the beams 25are fully raised.

FIG. 2 is essentially identical to FIG. with the same reference numeralsbeing used for identical structure whenever applicable.

After leaving the welding unit 4 the band 18 passes between two sets oftensioning rollers 19 flanking a straightener 20. Thereafter the bandpasses through a storage area 21 and into a pickling bath 22, whence itpasses through the drive 6, the bending units 8a 8f, the straighteners16a and 16b, the rolling apparatus 17 and the drive 7 to another storagearea 23. A galvanizing station 31 is provided immediately downstream ofthe storage area 23 followed by another pair of tensioning rollers 24,the shear 5, and the takeup spool 2.

In this embodiment, however, all of the rolls 9 are of the samediameter, as are the rolls 110, and so on. A decrease in the bendingradius in the transport direction is obtained exclusively by tilting theplane of the axes of the upper rolls relative to that of the lower rollswith the cylinders 26 and 27.

FIG. 5 shows how the band passes through three rolls 9. Were the band 18perfectly elastic it would assume the position shown by dashed lines 28,engaging the middle roll over an arc a of 65. However, the inherentstiffness of the band 18 causes it to assume a sinusoidal path betweentwo rolls so that it only engages the roll over an arc B of about 30. Instraighteners a much smaller contact are is used.

The are B should exceed 5 and are a should be greater than 25. Since area is substantially equal to that are defined with reference to themiddle rollers rotation axis by a pair of planes tangent to it and tothe neighboring rolls, it can be seen that adjustment can be achievedeither by displacing the rolls toward each other in the transportdirection ,or raising or lowering every other roller relative to itsneighbors. This latter method is the most efficient and practicalsolution.

In the apparatus according to the present invention the band is madelonger, narrower, and thinner as it passes through the several bendingunits. In the first bending unit the thickness may be decreased byaround 70 percent while the width is reduced by 30 percent withoutexceeding the brittle-fracture point. In the fol lowing units, however,the relative reduction is of a lesser degree since the tensile strengthis increased and the reduced thickness, even with increasingly tighterbends, is less susceptible to flow during bending. Starting with a steelband of between 1 and 5 mm in thickness a device as shown in FIGS. 1 5can reduce its thickness depending on the setting of the rolls from to100 percent. The thicker bands are passed through all five bendingunits; thinner ones need only pass through the last three or four.Similarly, if the desired thickness is obtained, the last severalbending units may not be used.

SPECIFIC EXAMPLE The diameter D (in centimeters) is calculated accordingto the following formula:

D (h E)/(K k wherein it is the thickness of the band in centimeters, Eis the modulus of elasticity in kg/cm, k is the mean tensile strength inkg/cm and K is a constant between 25 and 50.

Employing a K equal to 35 with a steel band 3 mm thick having a meantensile strength of 2,500 kg/cm a roller diameter of 72 mm is used.Since this will reduce the thickness of the band, the other rollers arecalculated on the basis of reduction obtained. In the arrangement ofFIG. 2 a steel band of 3 mm thickness is longitudinally stressed at2,000 kg/cm and passed between the six rolling units whose rolls aredimensioned 80, 65, 50, 40, 30, and mm in diameter.

I claim: 1. A method of stretching a metallic band comprising the stepsof:

continuously advancing said band longitudinally along a transport path;longitudinally tensioning said band as it advances between twolongitudinally spaced locations along said path with a tension forcebelow the mean ten sile strength of the band in an unbent state; locallybending the advancing tensioned band between said locations through afirst radius of curvature sufficient to locally lower the mean tensilestrength of said band at the bend below the tension force therebyelongating the bent portion; and locally bending the advancing tensionedband at a location downstream of the first bending thereof through asecond radius of curvature smaller than said first radius to locallylower the mean tensile strength of said band again and to permit localplastic elongation of said band.

2. The method defined in claim I wherein said band is bent withoutcompression being exerted thereon at the headings.

3. The method defined in claim 1, further comprising the steps ofcold-rolling and straightening the band after elongation thereof.

4. The method defined in claim 1 wherein said band is longitudinallytensioned at at most of its mean tensile strength.

5. The method defined in claim 1 wherein said band is bent over rollsspaced one after the other along the transport path, said method furthercomprising the step of situating said rolls such that said band engageseach roll over an actual contact arc greater than 5.

6. An apparatus for stretching a metallic band comprising:

means for continuously advancing the band longitudinally along atransport path;

means at an upstream end and at a downstream end of said path forlongitudinally tensioning said band with a tension force below the meantensile strength of said band;

a first bending roll along said path of a predetermined diameter;

means for locally bending said band around said first roll to conformsame thereto;

a second bending roll along said path downstream of said first roll andof a diameter smaller than the diameter of said first roll; and

means for locally bending said band around said first roll to conformsame thereto. I

7. The apparatus defined in claim 6 wherein each of said means forlocally bending said band includes a pair of guide rolls flanking therespective bending roll.

8. The apparatus defined in claim 6 wherein each bending roll has adiameter D dimensioned according to the formula:

wherein h is the thickness in cm of the band fed to the respective guideroll, E is the modulus of elasticity of the band in kg/cm k is the meantensile strength of the band in kglcm and K is a constant between 25 and50.

9. The apparatus defined in claim 6 wherein each of said bending rollsengages said band over an arc of more than 5.

10. The apparatus defined in claim 9 wherein a pair of imaginary planespassing through said band and each tangent to a respective guide rolland both tangent along respective angularly offset tangent lines to therespective bending roll define between their tangent lines an arc ofmore than 25 on said blending roll.

11. The apparatus defined in claim 10, further comprising means fordisplacing said bending rolls transverse to said transport path foradjustment of said arcs. a: =1:

1. A method of stretching a metallic band comprising the steps of:continuously advancing said band longitudinally along a transport path;longitudinally tensioning said band as it advances between twolongitudinally spaced locations along said path with a tension forcebelow the mean tensile strength of the band in an unbent state; locallybending the advancing tensioned band between said locations through afirst radius of curvature sufficient to locally lower the mean tensilestrength of said band at the bend below the tension force therebyelongating the bent portion; and locally bending the advancing tensionedband at a location downstream of the first bending thereof through asecond radius of curvature smaller than said first radius to locallylower the mean tensile strength of said band again and to permit localplastic elongation of said band.
 2. The method defined in claim 1wherein said band is bent without compression being exerted thereon atthe bendings.
 3. The method defined in claim 1, further comprising thesteps of cold-rolling and straightening the band after elongationthereof.
 4. The method defined in claim 1 wherein said band islongitudinally tensioned at 80% at most of its mean tensile strength. 5.The method defined in claim 1 wherein said band is bent over rollsspaced one after the other along the transport path, said method furthercomprising the step of situating said rolls such that said band engageseach roll over an actual contact arc greater than 5*.
 6. An apparatusfor stretching a metallic band comprising: means for continuouslyadvancing the band longitudinally along a transport path; means at anupstream end and at a downstream end of said path for longitudinallytensioning said band with a tension force below the mean tensilestrength of said band; a first bending roll along said path of apredetermined diameter; means for locally bending said band around saidfirst roll to conform same thereto; a second bending roll along saidpath downstream of said first roll and of a diameter smaller than thediameter of said first roll; and means for locally bending said bandaround said first roll to conform same thereto.
 7. The apparatus definedin claim 6 wherein each of said means for locally bending said bandincludes a pair of guide rolls flanking the respective bending roll. 8.The apparatus defined in claim 6 wherein each bending roll has adiameter D dimensIoned according to the formula: D (h . E)/(K . kF)wherein h is the thickness in cm of the band fed to the respective guideroll, E is the modulus of elasticity of the band in kg/cm2, kF is themean tensile strength of the band in kg/cm2, and K is a constant between25 and
 50. 9. The apparatus defined in claim 6 wherein each of saidbending rolls engages said band over an arc of more than 5*.
 10. Theapparatus defined in claim 9 wherein a pair of imaginary planes passingthrough said band and each tangent to a respective guide roll and bothtangent along respective angularly offset tangent lines to therespective bending roll define between their tangent lines an arc ofmore than 25* on said bending roll.
 11. The apparatus defined in claim10, further comprising means for displacing said bending rollstransverse to said transport path for adjustment of said arcs.